01 - Preheat oven to 350°F. Grease and lightly flour a 9-inch round or square cake pan, tapping out any excess flour.
02 - In a large mixing bowl, mash the ripe bananas until mostly smooth. Add the vegetable oil, granulated sugar, eggs, and vanilla extract, then beat together until well blended and creamy.
03 - In a separate medium bowl, whisk together the all-purpose flour, baking soda, baking powder, salt, and ground cinnamon until evenly distributed.
04 - Gradually add the dry ingredient mixture to the wet ingredients, folding gently with a spatula until just combined. Stop mixing as soon as no dry streaks remain to keep the cake tender.
05 - If using chopped nuts or chocolate chips, gently fold them into the batter until evenly distributed.
06 - Pour the batter into the prepared cake pan and smooth the top with a spatula to create an even layer.
07 - Bake on the center rack for 35 to 40 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
08 - Let the cake cool in the pan for 10 minutes, then turn it out onto a wire rack to cool completely before slicing and serving.